Electric induction furnace



Feb. 25, 1930. w. ESMARCH ELECTHIG INDUCTION FURNACE Filed Nv. 21, 1928 ML. Y ding Md Hau E-sqARcrl ATToRNE s.

' Patented Feb. 25, 1930 UNITED STATES PATENT OFFICE WIIiHEIM ESMABGH, OF BERLIN-HALENSEE, GERMANY, ASSIGNOR- TO SIEMENS .80 HALSKE, AKTIENGESELLSCHAFT, OF SIEMENSSTADT, NEAR BERLIN, GERMANY, A

CORPORATION OF GERMANY nmac'rmc nmuc'rron rnnnacn Application filed November 21, 1928, Serial No. 320,790, and in Germany December 8, 1927.

This invention relates to electric. induction furnaces, particularly of the air-core or so-called ironless type. Furnaces of this type, when intended for operation with highfrequency currents, are generally made with a primary coil consisting of a copper tube through which flows a cooling medium, preferably air or water. This well-known arrangement entails considerable losses, particularly on account of the Joule heat, since the skin effect causes the high-frequency currents to be crowded together on the inner side of the copper tube. Owing to this, the arrangement ust referred to is of relatively low efliciency.

It has also been proposed to construct the furnace coil of a plurality of thin copper strips placed upright on edge and insulated from one another, the outside air alone being relied upon to cool this coil. Practical tests have shown that furnaces embodying this construction will permit only a small load on the coil. I

According to the present invention, the drawbacks mentioned above are avoided by employing a coil made of solid material immersed in an insulating li uid, preferably oil, the best results being 0 tained when a continuous flow of such liquid is maintained. A very convenlent arrangement conslsts in placing the coil within atubular container in such a manner as to permit the coil to be lifted out readily.

Without desiring to limit myself to the specific details shown, I will now describe a satisfactory and typical embodiment of my invention, as illustrated by the accompanying drawings, in which Fi 1 is a. diagrammatic side elevation of one rm of my invention, the furnace being shown in central vertical section; Fig. 2 is a horizontal section on the line A-B of Fig. 1; Fig. 3 is a plan view of one windin of the induction coil.

In the high frequency induction furnace illustrated, the induction coil proper 8 consists of two thin strips of solid copper insulated from each other, placed edgewise, and wound in such amanner that their flat sides lie in cylindrical surfaces. The two strips are crossed repeatedly in regular fashion as shown in Fig. 3 and are supported on a suit able insulating carrier 2', shown as an openwork carrier consisting of spaced upright rods, preferably notched to receive the coiled copper strips. The two strips which form the induction coilare shown in Fig. 1 connected in parallel. The subdivision of the coil and the crossing of the individual parts of the coil permits a better heating effect for a' given cross section of the copper. The coil 8 and its carrier 11 constitute a unit which can be handled bodily to insert it into a tubular container 6 or to lift it therefrom, after taking off the removable cap a of this container. An insulating liquid, preferably oil, is caused to flow through said container, being preferably admitted at the bottom, as indicated at e, and passing out at the top, through an outlet a. It is advisable to employ the same body of oil continuously, by causing it to return from the outlet at to the inlet 6, a cooler d being associated with the return conduit f, which may also contain a pump 9 to propel the liquid, although circulation might also be accomplished without the pump, on the thermo-siphon principle. It will be noted that almost the entire inner and outer surfaces of the coil 8 are in con tact with the coolin and insulating liquid.

The parts descri ed above are associated in any suitable manner with the furnace or crucible proper, that is to say, the chamber adapted to receive the material to be melted or heated. In Figs. 1 and2, the container b surrounds the furnace pro or or crucible t. It is also possible to make t e container 6 of a smaller diameter than the crucible t, and place it within the same. In this case, the outer field of the coil 8 is utilized as well as its inner field, so that the efliciency of the arrangement is even greater than in Figs. 1 and 2, where only the inner field of the coil produces the heating efl'ect. The container 6 is preferably made of insulating material, for instance fiberboardbr the like.

WhileI have referred articularly to the use of my invention for 'gh frequency induction furnaces, I do not wish to restrict myself thereto, since the improvement is applicable as well to low frequency furnaces of the ironless type. It will be understood that various modifications may be made without departing from the nature of my invention asset forth in the appended claims.

I claim 1. In an ironless electric induction furnace, a tubular container, and an induction coil consisting of solid conductin material, located within said container, sai coil comprisin a plurality of strips insulated from each ot er and crossed repeatedly.

2. In an ironless electric induction furnace, a tubular container, and an induction coil consisting of solid conducting material, located within said container, said coil comprising a plurality of strips insulated from each other, and wound in cylindrical fashion, said strips bein crossed repeatedly.

3. In an ironless electric induction furnace, a tubular container having an inlet and an outlet for a coolin liquid, an induction coil consistin of soli conductin material, located wit in said container,an an open-work carrier for said 'coil, consisting of spaced members enga 'ng the coil at intervals, said carrier being li ewise located within said container and forming with said coil a structural unit readily removable from said container, and an inlet and an outlet at said container for an insulating liquid.

4. In an ironless induction furnace, a tubular container and an induction coil consisting of solid conductin material, located within said container, sald coil comprising a plurality of strips insulated from each other and crossed repeatedly and wound in cylindrical fashion, and an outlet and an inlet at said container for the circulation of insulating oil.

In testimony whereof I afiix m si ature.

WILHELM ES CH. 

